Metal-ceramic bond

ABSTRACT

A method of connecting a metal ( 1 ) with a ceramic material ( 2 ) comprises the steps of providing a through-hole ( 3 ) in the ceramic material and positioning the metal ( 1 ) to be connected to the ceramic material ( 2 ) proximate to the ceramic material ( 2 ) with the through-hole ( 3 ). Subsequently, the metal ( 1 ) is melted ( 7 ) proximate to the through-hole ( 3 ). A pressure difference prevails between the side of the ceramic ( 2 ) remote from the metal and the side of the metal ( 1 ) remote from the ceramic material ( 2 ). A larger pressure prevails at the side of the metal ( 1 ) remote from the ceramic material ( 2 ). The pressure difference causes the melt ( 7 ) to be pressed into the through-hole ( 3 ) in the ceramic material ( 2 ). The through-hole ( 3 ) has such a shape that, after solidification, the solidified material ( 14 ) and the through-hole ( 3 ) have a complementary locking form.

The invention relates to a method of connecting two different materials,the method comprising the steps of providing a through-hole in onematerial, melting the other material proximate to the through-hole andsubsequently allowing it to solidify in the through-hole.

The invention also relates to a composite structure of a metal and anon-metal part.

Such a method and composite structure are known from the U.S. Pat. No.5,498,850. This patent describes a structure comprising a metal plateand a plate of semiconductor material, the metal plate having athrough-hole. The semiconductor material is subsequently illuminatedwith an intensive laser beam via the through-hole and caused to melt.The molten semiconductor material also causes a part of the metal tomelt. The molten metal forms an alloy with the molten semiconductormaterial. The alloy is not resistant in air and must be provided with aseparate cover layer.

The method described has the drawback that it has various stages anddoes not offer a solution for connecting a metal and a ceramic material.

It is an object of the invention to provide a method and a compositestructure as described above, in which a reliable bond between theceramic material and the metal is achieved with great positionalaccuracy and temperature stability.

To this end, a method according to the invention is characterized inthat one material is a ceramic material, in that the other material is ametal and in that, in the molten state of the metal, a pressuredifference prevails between the side of the metal remote from theceramic material and the side of the ceramic material remote from themetal, a larger pressure prevailing on the side of the metal remote fromthe ceramic material.

According to the invention, a composite structure is characterized inthat the non-metal part is a ceramic part, in that the ceramic part isprovided with a through-hole and in that, in the molten state, the metalpart has penetrated the through-hole and has solidified.

In this way, the penetration of the molten metal in the through-hole isbrought about in an active manner. It is also achieved that no specialadaptations to the materials and no time-consuming process, such asthermal compression, are necessary.

A preferred embodiment of a method according to the invention ischaracterized in that, after the metal has been caused to melt proximateto the through-hole, the pressure difference is brought about by causingthe molten metal on the side of the metal remote from the ceramicmaterial to evaporate.

This means that no materials and resources other than the metal and theceramic material itself or means for causing the metal to melt andevaporate are necessary.

A preferred embodiment of the method according to the invention isfurther characterized in that the evaporation takes place by subjectingthe side of the molten metal remote from the ceramic material to laserradiation which causes a surface layer of the molten metal to evaporate.

This means that a single laser of sufficient power can be used, firstwith a relatively low power to cause the metal to melt proximate to thethrough-hole and then, when the metal has melted, to apply a high-powerlaser pulse to the melt so that a surface layer of the melt evaporates.The evaporating metal ensures an increase of pressure as a result ofwhich the melt is pressed into the through-hole. In addition to theincrease of pressure, the fact that the evaporating metal carries withit a pulse directed away from the metal and the ceramic material, as aresult of which the metal in the melt receives a pulse in the directionof the through-hole, will also play a role.

The further preferred embodiment of a method according to the inventionis characterized in that, due to the solidification of the molten metal,a locking form is created between the metal and the ceramic material.

It is known that, in general, metal and ceramic material never or hardlyever adhere to each other. Adhesion, if occurring at all, takes place ata high temperature, with the ceramic material and the molten metalhaving approximately the same temperature.

It is achieved by the present preferred embodiment of the methodaccording to the invention that the ceramic material and the moltenmetal do not need to have substantially the same high temperature inorder to bring about the bond. Due to the locking form created after thesolidification of the molten metal, the strength of the bond between themetal and the ceramic material is almost exclusively determined by thestrength of the locking form.

The invention will now be elucidated with reference to the accompanyingdrawings in which:

FIG. 1 shows a metal and a ceramic part;

FIG. 2 shows the step of melting the metal;

FIG. 3 shows the step of applying a pressure difference;

FIG. 4 shows the bond between the metal and the ceramic part;

FIG. 5 shows another embodiment of a bond between the metal and theceramic part;

FIG. 6 shows a stop means;

FIG. 7 shows the power of a laser pulse as a function of time;

FIG. 8 shows an alternative manner of applying a pressure difference.

In FIG. 1, reference numeral 1 denotes a metal part and referencenumeral 2 denotes a ceramic part. The ceramic part 2 is provided with athrough-hole 3 with walls 4 tapering in the direction of the metal part.The metal part 1 and the ceramic part 2 are shown in FIG. 1 by way ofexample as a cross-section of two flat plates. The plates 1 and 2 may ofcourse also be curved and the parts 1 and 2 can also have a shape otherthan flat.

In FIG. 2, reference numeral 5 denotes a laser beam which, in thedirection of the arrow 6, engages the metal part 1 on the side remotefrom the ceramic part 2. The laser beam 5 has such an intensity that themetal part 1 at the location of the through-hole 3 is caused to melt,which is indicated by melt 7. The intensity of the laser beam 5 is notsufficient to cause the melt 7 to boil. The resultant situation isstable. It is to be noted that the space 8 in the Figures between themetal part 1 and the ceramic part 2 is not relevant to the invention andis preferably absent. The space 8 is only shown in the Figures toillustrate the difference between metal part 1 and ceramic part 2.

After the laser beam 5 has created the melt 7, the intensity of thelaser beam 5 is increased for a short time, as is indicated by thearrows 9, to such a level that a surface layer 10 of the melt 7evaporates to a vapor cloud which is denoted by reference numeral 11.The extension of the vapor cloud 11 in the direction away from the metalpart 1 has the result that a force, as indicated by the arrow 12, isexerted in the direction of the ceramic part 2 on the surface 10 of themelt 7, as is indicated by arrow 13. As a result, the melt 7 moves inthe direction of the arrow 13 and therefore in the direction of thethrough-hole 3. After a short time, the laser beam 5 is switched off andthe melt 7 has penetrated the through-hole 3. As a result of switchingoff the laser beam 5, the melt 7 will cool down and solidify and asolidified material 14 will be formed, as is shown in FIG. 4.

FIG. 4 shows that the solidified material 14 along with the taperingwall 4 of the through-hole 3 constitutes a locking form. The lockingform ensures that the metal part 1 and the ceramic part 2 are bondedfirmly together via the solidified material 14.

The bond thereby achieved between the metal part 1 and the ceramic part2 has a high level of positional accuracy, namely the accuracy withwhich the through-hole 3 is provided in the ceramic part 2 and theaccuracy with which the ceramic part 2 provided with the through-hole 3and the metal part 1 are positioned in relation to each other. The bondachieved in this way also has a greater temperature stability. As longas the solidified material 14, and thus the metal part 1, do not melt,the metal part 1 and the ceramic part 2 retain the relative positionsthey took when the melt 7 turned into solidified material 14.

It will be evident from the foregoing that neither the metal part 1 northe ceramic part 2, with the exception of the provision of thethrough-hole 3, have undergone any process. In particular, neither parthas undergone a surface treatment or a surface treatment with anothermaterial such as a flux or a bonding agent.

It will further be evident from the above description that no additionalmaterials are necessary in order to bring about the bond. In particularit is to be noted that no solder or other third material is necessary inorder to form the bond between the metal part 1 and the ceramic part 2.

In the embodiments shown in FIGS. 1 to 4, the through-hole 3 is shown asan opening tapering in the direction of the metal part 1. For thoseskilled in the art, openings with a form other than a taper will alsoyield a locking form between the solidified material 14 and the ceramicpart 2. A particular shape of a locking form within the context of thepresent invention is shown in FIG. 5. In FIG. 5, the through-hole 3 hasstraight walls 4 and the locking form is formed in that the melt 7, as aresult of the pressure difference applied between the side of the metalpart 1 remote from the ceramic part and the side of the ceramic part 2remote from the metal part 1, where the larger pressure prevails on theside of the metal part 1 remote from the ceramic part 2, the melt 7 ispushed through the through-hole 3 and then flows over the edge 15 andthen solidifies into the solidified material 14. Together with the edge15, the edge 16 of the solidified material 14 that protrudes over theedge 15 constitutes a locking form that secures the solidified material14, the metal part 1 and the ceramic part 2 to each other.

In the event that the pressure difference is too great and/or is presenttoo long, there is a risk that the melt 7 will be pushed completelythrough the through-hole 3 and that no bond at all will be createdbetween the metal part 1 and the ceramic part 2. FIG. 6 shows a solutionto this problem. Right under the through-hole 3, a stop means 21 isprovided. In connection with the high temperatures of the melt 7 and inconnection with the desire that the melt 7 should not adhere to the stopmeans 21, at least the part of the surface of the stop means 21 facingthe through-hole 3 is manufactured of a ceramic material, or the stopmeans 21 is manufactured of a material having a high thermalconductivity coefficient. The larger the temperature difference betweenthe melt 7 and the ceramic material 2, the smaller the risk that themelt 7 will adhere to a ceramic surface of the stop means 21. Atemperature difference of more than 50° C. between the melt 7 and theceramic material of the stop means 21 is generally sufficient to ensurethat the melt 7 does not adhere to the stop means 21 at hightemperatures. If the stop means 21 is made of a material having a highthermal conductivity coefficient, the molten metal that penetrates thehole 3 will cool down so quickly on contact that there is no or nosignificant adhesion.

FIG. 8 shows another way of achieving a pressure difference between theside of the metal part 1 remote from the ceramic part 2 and the side ofthe ceramic part 2 remote from the metal part 1. Around the through-hole3, a holder 18 is positioned against the ceramic part 2 by means of anO-ring 17. The holder 18 is connected by means of a connecting tube 19to a device 20 for generating a sub-atmospheric pressure in the holder18. After a melt 7 has been created in the metal part 1 opposite to thethrough-hole 3, the device 20 ensures that there is a short-lastingsub-atmospheric pressure in the holder 18. As a result of the pressuredifference, the melt 7 is pressed into the through-hole 3. The pressuredifference is then reduced again as a result of which the melt 7 doesnot penetrate the hole 3 any further and the melt 7 is cooled to formthe solidified material 14.

In the embodiment shown in FIG. 8, the stop means 21 may be positioned,for example, rigidly in the holder 18.

FIG. 7 shows by way of example the progress as a function of time of thepower of a laser pulse as described within the context of FIGS. 2 and 3,but also applicable in the embodiments shown in FIGS. 5, 6 and 8.

For a period of about 14 ms, the laser pulse is maintained at a power P1of about 350 W. As a result, the metal part 1 melts across a certaindiameter, for example 600 μm. The resultant melt is clean and free frompeaks. Then a short-lasting laser pulse with a power of P2 is directedfor 0.1-0.3 ms towards the melt. Depending on, amongst other things, thewidth of the crack between the metal part 1 and the ceramic part 2 andthe diameter of the melt 7, the power P2 ranges between 700 W and 2.5kW. This short-lasting high-power pulse results in a short-lastingevaporation to the vapor cloud 11 (see FIG. 3). The formation of thevapor cloud leads to the exertion of a pressure on the melt 7 in thedirection of the hole 3 in the ceramic part 2.

EXAMPLE

In a device held in an electron source in a vacuum it is necessary toconnect a metal plate, which forms a grid in the electron source, and aceramic plate with great positional accuracy and temperature stability.Both plates are flat and are connected together at various points. Theplates have a thickness of between 250 and 380 μm and dimensions of theorder of 1 cm. The through-holes 3 have a diameter of between 260 and400 μ. The ceramic material is A12O3. The laser beam 5 has a power ofbetween 300 and 700 W and irradiates the metal for a period of 10 to 15ms. The laser beam 5 has a spot size of approximately 600 μm. Asub-atmospheric pressure of 120 to 160 mb prevails in the holder 18. Theslope of the walls 3 of the through-hole 4 is 20° to the normal.

The given values provide the possibility of creating the metal-ceramicbond between the metal part 1 and the ceramic part 2 with a highpositional accuracy and a high temperature stability. Likewise, the useof the metal to be bonded itself as the basic part for the melt ensuresthat no contamination by, for example, solder or another flux can occur.The use of the metal itself to create the melt without the addition ofother materials also has the effect that the bond is extremely robust.The positional accuracy is fully determined by the accuracy with whichthe metal part and the ceramic part are positioned and retained inrelation to each other prior to connection.

After the foregoing description, many embodiments and modifications willbe evident to those skilled in the art. All of these modifications andembodiments are considered to be within the scope of the invention.

1. A method of connecting a metallic material with a ceramic material,comprising: providing a through-hole in the ceramic material; disposingthe metallic material proximate to the through-hole of the ceramicmaterial; producing molten metal by melting at least a portion of themetallic material adjacent to the through-hole of the ceramic material;and facilitating at least a portion of the molten metal to pass throughthe through-hole by causing a pressure difference between a first areaon a side of the metallic material remote from the ceramic material anda second area on a side of the ceramic material remote from the metallicmaterial, such that pressure is higher in the first area than in thesecond area.
 2. The method of claim 1, wherein the pressure differenceis at least partially created by applying a sub-atmospheric pressure onthe side of the ceramic material remote from the metallic material. 3.The method of claim 1, wherein the pressure difference is at leastpartially created by applying a pressure above atmospheric pressure onthe side of the metallic material remote from the ceramic material. 4.The method of claim 3, wherein, after said melting, the pressuredifference is at least partially created by causing some of the moltenmetal on the side of the metallic material remote from the ceramicmaterial to evaporate.
 5. The method of claim 4, wherein the evaporationis at least partially caused by subjecting the side of the molten metalto laser radiation which causes a surface layer of the molten metal toevaporate.
 6. The method of claim 1, including allowing the molten metalto solidify to form a locking form between the metallic material and theceramic material.
 7. The method of claim 1, wherein, during the periodwhen the pressure difference prevails, a stop means is present oppositethe through-hole on the side of the ceramic material remote from themetallic material.
 8. The method of claim 7, wherein the surfacematerial of the stop means is non-adhesive in relation to the moltenmetal.
 9. The method of claim 8, wherein the surface material of thestop means is a ceramic material.